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HOUSTON -- NASA and its international partners have assigned the International Space Station's crew members through 2010. The numbering sequence of expeditions was modified to reflect the start of six-person crews.

The update to the expedition numbering begins with the docking of a Soyuz spacecraft in May 2009. That Soyuz will mark the beginning of six-person crew operations. From that point forward, expeditions will end with the undocking of a Soyuz. The expedition number will change every two to four months as new crew members arrive and depart.

The arrangement emphasizes that every six-person crew living on the station is a cohesive team. A crew member typically will stay about six months and be part of two expeditions. In addition to the Russian Soyuz, the space shuttle will continue to provide transportation for station crew members through mission STS-129, targeted for the fall of 2009.

With the departure of a Soyuz, command of the station will be handed over to a crew member remaining aboard, and the next expedition will begin. Specific backup crew members will not be announced because of the streamlined training flow for six-person crews. If needed, backups can be selected from subsequent crews in training.

The groups of assigned crew members, beginning with the first six-person crew and including newly announced crew members, are outlined below by expedition. An asterisk indicates the crew member was previously announced.

Expedition 20 begins with the Soyuz 19 docking and the arrival of three new crew members in May 2009. - Russian cosmonaut Gennady Padalka, International Space Station commander, who will launch in March 2009 on Soyuz 18 and return in October 2009 on Soyuz 18.* - NASA astronaut Michael R. Barratt, who will launch in March 2009 on Soyuz 18 and return in October 2009 on Soyuz 18.* - NASA astronaut Tim Kopra, who will launch on STS-127 and return on STS-128.* - Russian cosmonaut Roman Romanenko, who will launch in May 2009 on Soyuz 19 and return in November 2009 on Soyuz 19. - European Space Agency, or ESA, astronaut Frank De Winne, who will launch in May 2009 on Soyuz 19 and return in November 2009 on Soyuz 19* - Canadian Space Agency, or CSA, astronaut Robert Thirsk, who will launch in May 2009 on Soyuz 19 and return on STS-129.* - NASA astronaut Nicole Stott, who will launch on STS-128 and return in November 2009 on Soyuz 19.*

Expedition 21 begins with the Soyuz 18 undocking in October 2009. Two new crew members will arrive on Soyuz 20 for the handover before the previous crew departs. - ESA astronaut Frank De Winne, the first European Space Agency station commander - CSA astronaut Robert Thirsk - Russian cosmonaut Roman Romanenko - NASA astronaut Nicole Stott - Russian Cosmonaut Maxim Suraev, who will launch in September 2009 on Soyuz 20 and return in March 2010 on Soyuz 20 - NASA astronaut Jeffrey N. Williams, who will launch in September 2009 on Soyuz 20 and return in March 2010 on Soyuz 20.

Expedition 22 begins with the Soyuz 19 undocking in November 2009. Three new crew members will arrive shortly thereafter on Soyuz 21. - NASA astronaut Jeffrey N. Williams, station commander - Russian cosmonaut Maxim Suraev - Russian cosmonaut Oleg Kotov, who will launch in December 2009 on Soyuz 21 and return in May 2010 on Soyuz 21. - Japan Aerospace Exploration Agency, or JAXA, astronaut Soichi Noguchi, who will launch in December 2009 on Soyuz 21 and return in May 2010 on Soyuz 21.* - NASA astronaut T.J. Creamer, who will launch in December 2009 on Soyuz 21 and return in May 2010 on Soyuz 21.*

Expedition 23 begins with the Soyuz 20 undocking in March 2010. Three new crew members will arrive shortly thereafter on Soyuz 22. - Russian cosmonaut Oleg Kotov, station commander - JAXA astronaut Soichi Noguchi - NASA astronaut T.J. Creamer - Russian cosmonaut Alexander Kaleri, who will launch in April 2010 on Soyuz 22 and return in September 2010 on Soyuz 22. - Russian cosmonaut Mikhail Kornienko, who will launch in April 2010 on Soyuz 22 and return in September 2010 on Soyuz 22. - NASA astronaut Tracy E. Caldwell, who will launch in April 2010 on Soyuz 22 and return in September 2010 on Soyuz 22.

Expedition 24 begins with the Soyuz 21 undocking in May 2010. Three new crew members will arrive shortly thereafter on Soyuz 23. - Russian cosmonaut Alexander Kaleri, station commander - Russian cosmonaut Mikhail Kornienko - NASA astronaut Tracy E. Caldwell - Russian cosmonaut Alexander Skvortsov, who will launch in May 2010 on Soyuz 23 and return in November 2010 on Soyuz 23. - NASA astronaut Shannon Walker, who will launch in May 2010 on Soyuz 23 and return November 2010 on Soyuz 23. - NASA astronaut Douglas H. Wheelock, who will launch in May 2010 on Soyuz 23 and return in November 2010 on Soyuz 23.

Expedition 25 begins with the Soyuz 22 undocking in September 2010. Three new crew members will arrive shortly thereafter on Soyuz 24. - NASA astronaut Douglas H. Wheelock, station commander - Russian cosmonaut Alexander Skvortsov - NASA astronaut Shannon Walker - Russian cosmonaut Dmitri Kondratyev, who will launch in September 2010 on Soyuz 24 and return in March 2011 on Soyuz 24. - Russian cosmonaut Oleg Skripochka, who will launch in September 2010 on Soyuz 24 and return in March 2011 on Soyuz 24. - NASA astronaut Scott J. Kelly, who will launch in September 2010 on Soyuz 24 and return in March 2011 on Soyuz 24.

Expedition 26 begins with the Soyuz 23 undocking in November 2010. Three crew members will arrive shortly thereafter on Soyuz 25. - NASA astronaut Scott J. Kelly, station commander - Russian cosmonaut Dmitri Kondratyev - Russian cosmonaut Oleg Skripochka - Russian cosmonaut Andrey Borisienko, who will launch in November 2010 on Soyuz 25 and return in May 2011 on Soyuz 25. - NASA astronaut Catherine Coleman, who will launch in November 2010 on Soyuz 25 and return in May 2011 on Soyuz 25. - ESA astronaut Paolo Nespoli, who will launch in November 2010 on Soyuz 25 and return in May 2011 on Soyuz 25.